Magnetic fields are present around all electrical equipment and power lines. Although we cannot see or feel them, these fields interact with the components inside the equipments, causing a slow undulation of displayed images, frequently described as swimming, shimmy, jitter or even hula, making the screen illegible. In addition, magnetic interference may generate incorrect data, operator eyestrain, operator fatigue and disability.
Unlike X-rays and light rays, magnetic fields do not travel in straight lines. Magnetic field lines are continuous curves, emitting from a source of field and eventually returning to the point of origin.
Therefore, shielding is essential in electronic equipments and various kinds of equipments radiating undesired magnetic waves; thus, the radiation of the electromagnetic waves and invasion of the electromagnetic waves from the exterior is prevented.
A magnetic shield is traditionally made of a metallic material such as steel, iron, and nickel. Because metallic materials have a strong attraction for magnetic fields, the shield traps the magnetic force and diverts it around the equipment generating heat. In addition, lead, for example, is extremely hazardous, heavy, and is very expensive to produce. Steel requires massive amounts of refinement; it is heavy, and prone to corrosion. Alloys of steel, iron, copper and nickel are very expensive to produce and will corrode quickly. Furthermore, the cost of forming these materials into shapes for current shielding is high as well as dangerous.
As components of equipments are made more sensitive, susceptibility to magnetic waves increases dramatically; thus, the prior art developed a variety of materials for the shield.
The prior art shows the use of plates of a metal having high magnetic permeability and saturation magnetic flux density such as permalloy. Unfortunately, shields made of this material are bulky and heavy. In addition, in most of the cases, it is necessary to cut, bend, or even weld the plates. This is a laborious and expensive process.
Furthermore, the prior art shows the use of paramagnetic materials (e.g. titanium) to encapsulate and shield medical devices due to their low magnetic susceptibilities. These materials operate by deflecting electromagnetic fields. However, although paramagnetic materials are less susceptible to magnetization than ferromagnetic materials, they can also produce unwanted images due to eddy currents generated by externally applied magnetic fields, such as the radio frequency fields used in the MRI procedures. These eddy currents produce localized magnetic fields, which disrupt and distort the magnetic resonance image. In addition, since the paramagnetic materials are electrically conductive, the eddy currents produced in them can result in ohmic heating and injury to the patient or the medical device.
As steel, iron, and nickel are ferrous materials, saturation of these materials will occur after a period of time being exposed to magnetic fields.
In recent years, Mu-Metal is considered the premier shielding material for electronic devices. Mu-Metal is the generic name for a high-permeability, magnetically “soft” alloy used for magnetic shielding. It includes about 80% nickel and 15% iron, with the balance being copper, molybdenum or chromium, depending on the recipe being used. Unfortunately, Mu-Metal material is very expensive. In addition, the Mu-metal contains ferrous materials; thus, the shield will become saturated, becoming a magnet itself, thus not useful as a shield.
The present inventors have seen the necessity of providing a magnetic shielding material that overcomes the above disadvantages. In addition, the present inventors have seen the necessity of providing a magnetic shield that does not trap the magnetic forces. Furthermore, the present inventors have seen the necessity of providing an inexpensive magnetic shielding material for a magnetic shield.